1. Technical Field
The present invention relates to wireless communications and, more particularly, to management of coverage areas by access nodes in wireless communication systems.
2. Description of Related Art
a. EV-DO Generally
Many people use mobile stations, such as cell phones and personal digital assistants (PDAs), to communicate with cellular wireless networks. These mobile stations and networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless communication protocol such as Code Division Multiple Access (CDMA), perhaps in conformance with one or more industry specifications such as IS-95 and IS-2000. Wireless networks that operate according to these specifications are often referred to as “1xRTT networks” (or “1x networks” for short), which stands for “Single Carrier Radio Transmission Technology.” These networks typically provide communication services such as voice, Short Message Service (SMS) messaging, and packet-data communication.
Recently, service providers have introduced mobile stations and wireless networks that communicate using a protocol known as EV-DO, which stands for “Evolution Data Optimized.” EV-DO networks, operating in conformance with industry specification IS-856, provide high rate packet-data service (including Voice over IP (VoIP) service) to mobile stations using a combination of time-division multiplexing (TDM) on the forward link (from the network to mobile stations) and CDMA technology on the reverse link (from mobile stations to the network). Furthermore, some mobile stations, known as hybrid mobile stations or hybrid access terminals, can communicate with both 1x networks and EV-DO networks.
In the EV-DO context, a mobile station is typically referred to as an access terminal, while the network entity with which the access terminal communicates over the air interface is known as an access node. The access node typically includes a device known as a radio network controller (RNC), which is similar to a base station controller (BSC) in 1x networks. The access node also includes one or more base transceiver stations (BTSs) or “Node-Bs,” each of which include one or more antennas that radiate to define respective wireless coverage areas. Among other functions, the RNC controls one or more BTSs, and acts as a conduit between the BTSs and an entity known as a packet data serving node (PDSN), which provides access to a packet-data network. Thus, when positioned in one of these wireless coverage areas, an access terminal may communicate over the packet-data network via the access node and the PDSN.
b. Session Negotiation
To initiate connectivity, an access terminal requests what is known as a Universal Access Terminal Identifier (UATI) from an access node. The access node may respond by granting the access terminal a UATI, which then serves to identify the access terminal to the access node for some period of time. After acquiring a UATI, the access terminal will typically communicate with the access node over the air interface to set up what is referred to as a “session.” Essentially, an access terminal that has a session with an access node can engage in packet-data communication over the packet-data network to which the access node and the PDSN provide access. Conversely, an access terminal that does not have a session with an access node can not engage in packet-data communication over the packet-data network.
As part of setting up the session, the access terminal sends a connection request to the access node, requesting an air-interface connection. The access node will responsively work to establish the air-interface connection with the access terminal, which involves the access node instructing the access terminal to communicate with the access node over what is known as a traffic channel. This traffic channel takes the form of particular timeslots on the forward link, during which the access node sends data to the access terminal, and a particular CDMA channel on the reverse link, over which the access terminal sends data to the access node.
In addition to establishing the connection with the access terminal, the access node takes a number of other actions, one of which is to validate that the access terminal is authorized to engage in communication via the access node. Another such action is to set up a radio-packet (e.g., A10/A11) connection between the access node and the PDSN for the access terminal. The access node also facilitates establishment of a data link (e.g., a point-to-point protocol (PPP) connection) between the access terminal and the PDSN. Furthermore, an entity such as the PDSN or a Mobile-IP home agent assigns an IP address to the access terminal.
Once session negotiation (described further below) is complete, the access terminal has a session with the access node, and can therefore communicate over the packet-data network via the access node and the PDSN. Typically, the air-interface connection is then torn down (i.e. the access terminal goes from active to dormant), freeing up those resources for other access terminals. Both the network and the access terminal maintain data pertaining to the rest of what was established, however, including the IP address, radio-packet connection, and data link; in particular, the access terminal has a session (i.e. session data) maintained for it by the RNC.
Thereafter, if the access terminal wants to initiate packet-data communication, it sends another connection request to the access node, which then assigns a traffic channel to the access terminal. If the access node receives data addressed to the access terminal, the access node typically sends a page to the access terminal over a paging channel, and assigns a traffic channel to the access terminal. The access terminal can then communicate over the packet-data network, using the traffic channel, IP address, radio-packet connection, and data link.
c. Packet-Flow Types, Profile IDs, and Quality of Service (QoS) in EV-DO
In addition to VoIP communication, access terminals frequently engage in other types of packet-data communication, such as instant messaging (IM) and web browsing, among many types. Each instance of an access terminal engaging in a type of packet-data communication for a period of time may be deemed a “packet flow,” which would typically involve IP packets being sent and received by the access terminal. For example, a given VoIP call may be referred to as a VoIP packet flow. Thus, as examples, an access terminal may engage in VoIP packet flows, IM packet flows, push-to-talk (PTT) packet flows, streaming-audio packet flows, streaming-video packet flows, video-telephony packet flows, best-effort packet flows such as web-browsing and file-transfer-protocol (FTP) packet flows, and/or any other type(s).
To address the fact that access terminals engage in these various types of packet flows, a particular revision of EV-DO specifications, known as IS-856, Rev. A (“EV-DO-A”), provides for what are known as profile IDs, which are identifiers associated on a one-to-one basis with certain types of packet flows. IS-856, Revision A and IS-856, Release 0 are hereby incorporated herein by reference. Thus, one profile ID may be associated with VoIP packet flows, while another may be associated with PTT packet flows, and so on. Best-efforts packet flows typically do not have an associated profile ID, though they certainly could. And again, access terminals typically are able to engage in more than one type of packet flow, meaning that they can engage in one or more best-efforts packet flows and/or one or more profile-ID-associated packet flows. During (and typically near the end of) session negotiation, which may take on the order of four or five seconds (or longer), the access node and the access terminal negotiate a set of what are known as “personalities” for the access terminal. In particular, an access terminal and an access node may negotiate approximately five personalities, each of which is essentially a communication profile that is associated with a particular release or revision of IS-856, as well as with more specific functionality, and is often correlated with different types of packet flows having differing qualities of service (QoS). In general, providing a particular level of QoS essentially means providing a particular level of packet-forwarding (or “expedited-forwarding”) treatment to certain packet flows. Note that applying QoS is also known as “traffic shaping” or “DiffServ” (“differentiated services”), and is known in the art.
Once personality negotiation is complete, the access node and the access terminal then negotiate a set of profile IDs for the access terminal to use during the session; in other words, they agree as to the types of packet flows in which the access terminal is capable of engaging and in which the access terminal is permitted to engage during the session. During the session, when the access terminal is communicating via the access node according to the agreed-upon set of profile IDs, and in particular as part of setting up a packet flow, either the access terminal or the access node, or both, may send the other a message known as a ReservationOnRequest (RoR), which may include at least one profile ID, indicating the type of requested packet flow.
Once an RoR has been sent and acknowledged, the access terminal has an “open reservation” on the assigned traffic channel. This open reservation is associated with any profile IDs that were included in the RoR; in other words, the open reservation is associated with the type of packet flow in which the access terminal is able to engage. Note that an access terminal may have more than one open reservation on a traffic channel at one time, corresponding to the fact that the access terminal can engage in more than one packet flow at one time.